Abundant quantities of clean, fresh water have long been available in the United States. The unfortunate introduction of pesticides, pathogens, and highly volatile gasoline components, such as MTBE, into the aquifers of many drinking water systems is now a serious constraint to economic expansion in developed countries, and a matter of survival for 20% of the world's population. As an example, the U.S. Environmental Protection Agency announced Nov. 26.sup.th, 1997, that it will be issuing a new health advisory citing cancer data and drinking water contamination relating to MTBE, and will recommend maximum levels of 20-40 parts per billion in drinking water. There exists a need for cost effective method to reduce MTBE levels to meet these standards.
Current water purification technologies, including distillation, reverse osmosis, and carbon filtration usually produce suitable water quality, but their high capital, operating and maintenance costs have limited their use to only those situations where water shortages are most extreme or where cost is less important. Water contaminated with pesticide or gasoline contaminants are especially difficult and costly to remove with conventional technologies.
The $5.5 billion annual worldwide water purification market is growing, depending on market segment between 5% and 25% per year. Thirty-three percent (33% or $1.8 billion) is for purification of fresh water for commercial, industrial and residential use. Waste water reclamation and re-purification, currently about $1.0 billion annually, is the fastest growing segment. The overall market demand is currently constrained by the high cost of water purification products. Availability of low-cost alternatives could cause the market to reach $18 billion by the year 2002.
Both advantages and disadvantages of the prior art technologies are summarized below:
Vapor compression (VC), including distillation technology systems are positive on drinking water for both pathogen and chemical contamination remediation, remove total dissolved solids (TDS) and are excellent for desalinization. Drawbacks include a relatively high price, a generally large size, non portability and fairly complex construction and operation.
Reverse osmosis (RO) removes TDS with a relatively simple mechanism. Removal of non-volatile organics, pathogens is easy. However, the systems are subject to contaminating product water if feed water pressure and turbidity are out of operating parameters, involve a high price rate, does not remove dissolved organic compounds and are complex and sophisticated.
Air stripping (AS) is generally the least expensive form of water remediation and is fairly good at removing volatile organics. However, these systems are also large, very noisy and unsightly, do not remove non-volatile organics, do not remove pesticides or pathogens, depend on ancillary technology, like the use of granulated activated carbon (below), resulting in more O&M cost as well as air pollution (the volatile organics are transferred into the atmosphere).
Granulated activated carbon (GAC) acts positively on volatile and non-volatile organics like pesticides, is positive on pathogens, and can be reactivated in most cases. However, GAC also requires re-supply of heavy, bulky material, typically has a large adsorption ratio, such as about 1000 pounds GAC to 1 pound contaminant, and itself becomes a source of contamination of product water if allowed to saturate. Furthermore, saturated GAC is a hazardous waste product and must be handled as such, especially when considering issued including transportation, disposal or reactivation cost.
Low and medium pressure mercury vapor ultraviolet (UV) radiation is also effective at destroying pathogens, but only very slightly positive on organic or synthetic organic compounds at practical flow rates. Sometimes UV is used as part of a polishing loop on larger treatment systems. However, as a practical matter, use of UV radiation in the past has been impossible. These systems are not practical for chemically contaminated water, the required low pressure lamps are typically not self cleaning, would require hundreds of lamps to equal the dosage of a lamp of the present invention, and provide a larger footprint for any type of remediation application.
Ozone saturation is positive on pathogens and leaves no dangerous chemicals in the water. However, providing a system which injects ozone into a water supply or stream typically requires a physically rather large footprint and is complex to build and operate, involves high operation and maintenance costs, involves the production of ozone--a dangerous and reactive gas, and is not practical on chemical contaminants alone.
Finally, the use of chlorine (Cl) is known to render pathogens harmless pathogens but has no remedial effect on chemical contaminated water except for elimination of cyanides. Current competing technologies for chemical contamination of groundwater include reverse osmosis (RO), air stripping, and Activated Carbon filtration. Although the popularity of reverse osmosis has gained substantially in market share in recent years, different technology solutions continue to dominate the various niches. RO membrane production is dominated by a few companies (DuPont, Dow-Filmtec, Fluid Systems, Toyoba, etc.), but there are thousands of companies that act as integrators of RO systems. Few, with the notable exception of Ionics, Osmonics, and U.S. Filter exceed $100 million in revenues. Air stripping is less complicated and has low associated costs but is noisy, unsightly, pollutes the air, and has limited effectiveness in removing MTBE to EPA standard levels. Activated Carbon Filtration involves large quantities of carbon supplied by companies like Calgon, Inc.
Pathogen removal is accomplished with the addition of chlorine, distillation techniques, or the use of banks of low or medium pressure ultraviolet lamps. Distillation suppliers include large European, Japanese, and Korean contractors and this technology excels at the removal of TDS (total dissolved solids). Current ultraviolet lamp suppliers include Aquafine, Fisher & Porter, and Puress, Inc. There exists a need for technology which is more energy efficient and can simultaneously remove pathogens and chemical contamination. Such equipment could also be used to post-treat water at desalination facilities to remove chemical contaminants.
Traditional UV technology relies on low and medium pressure UV lamps, similar to the fluorescent lamps used in office buildings. Medium pressure lamps operate at higher power levels than do the low-pressure lamps and, consequently, are slightly more efficient than the standard low-pressure variety. The typical low-pressure power ranges from 30 to 100 watts while the medium pressures average 3000 watts. Both lamp types are known as atomic line radiators. They produce light energy in very narrow wavelength bands at 10-20% electrical efficiency. Both types operate with A/C current and are controlled by electrical ballast.
Though the lamp life is generally very long, maintenance cost are generally very high, especially in the case of low-pressure lamps. Cleaning is the main problem. Lamps become fouled in the water environment from precipitated dissolved solids and scum. This fouling action gradually reduces the UV output making the lamp useless. Therefore, these lamps must be removed on periodic bases and manually cleaned. Further more, low and medium pressure lamps do not produce the radiative power levels to effectively dissociate the chemical bonds of contaminants. They find their principle usage in the wastewater reclamation industry for biological degradation. At a single installation, these lamps are used hundreds and sometimes thousands at a time, thus amplifying the O&M cost.
Improvements to this type of technology include enhanced chemical doping of the lamp to increase its UV conversion efficiency, improved cold cathodes to increase lamp life and improved reaction chambers or effluent channels to maximize dosage and throughput and to minimize head loss.
The following U.S. patents are deemed relevant to the field of the present invention:
______________________________________ Patent No. Issue Date Inventor ______________________________________ 4,141,830 Feb. 27, 1979 Last 4,179,616 Dec. 18, 1979 Coviello et al. 4,230,571 Oct. 28, 1980 Dadd 4,273,660 Jun. 16, 1981 Beitzel 4,274,970 Jun. 23, 1981 Beitzel 4,437,999 Mar. 20, 1984 Mayne 4,595,498 Jun. 17, 1986 Cohen et al. 4,787,980 Nov. 29, 1988 Ackermann et al. 4,792,407 Dec. 20, 1988 Zeff et al. 4,836,929 Jun. 6, 1989 Baumann et al. 4,849,114 Jul. 18, 1989 Zeff et al. 4,849,115 Jul. 18, 1989 Cole et al. 4,913,827 Apr. 3, 1990 Nebel 4,124,051 Jun. 23, 1992 Bircher et al. 5,130,031 Jul. 14, 1992 Johnston 5,151,252 Sep. 29, 1992 Mass 5,178,755 Jan. 12, 1993 LaCrosse 5,308,480 May 3, 1994 Hinson et al. 5,466,367 Nov. 14, 1995 Coate et al. 5,330,661 Jul. 19, 1994 Okuda et al. 5,547,590 Aug. 20, 1996 Szabo ______________________________________
Last teaches an apparatus for purifying liquid such as water, in which as ultraviolet light source irradiates air passing through a first chamber surrounding the source, and then irradiates the liquid passing through the second chamber surrounding the first chamber. The air from the first chamber is ozonated by the UV light, and this air is bubbled into the water in the second chamber to maximize the purification through simultaneous ultraviolet and ozone exposure.
Beitzel teaches water treatment by passing a mixture of water and air and/or ozone through a nozzle which compresses and breaks up bubbles within the fluid mixture in a radiation housing, a hollow, cylindrical chamber located around an elongated UV light source. Beitzel also teaches water treatment by passing a thin film of water in contact with a bubble of air containing air and ozone while concurrently radiating both the water film and the air/ozone bubble with UV radiation.
Mayne teaches a method of feeding an insoluble organic solid material n the form of an organic resin or biological matter containing contaminating material such as radioactive waste from a nuclear facility or from treatment of animal or plant tissue in a laboratory or medical facility into a vessel containing water and, to which ultraviolet light and ozone, preferably by sparging, are applied.
Cohen et al. teaches a water purification system which includes an ion-exchange unit for producing high-resistivity water, followed by ozone exposure and ultraviolet sterilizer units that oxidize organics and also reduce resistivity, followed by a vacuum degassification unit to restore high resistivity.
Ackermann et al. is directed to a hydraulic multiplex unit for receiving continuously one or more samples of liquid from a liquid purification system distribution system and redirecting such sample or samples randomly or in sequence to one or more analytical instruments.
Zeff et al. teaches a method of oxidizing organic compounds in aqueous solutions by using in combination ozone, hydrogen peroxide and ultraviolet radiation. Zeff et al. also teaches a method of oxidizing toxic compounds including halogenated and/or partially oxygenated hydrocarbons and hydrazine and hydrazine derivatives in aqueous solutions by using in combination ozone, hydrogen peroxide and ultraviolet radiation.
Baumann et al. teaches a process for breaking down organic substances and/or microbes in pretreated feed water for high-purity recirculation systems using ozone which is generated in the anode space of an electrochemical cell and treated with ultraviolet rays and/or with hydrogen (H.sub.2) generated in the cathode space of the same cell or hydrogen (H.sub.2) supplied from outside, for use in reducing elementary oxygen in any form to harmless water.
Cole et al. teaches a process and apparatus for oxidizing organic residues in an aqueous stream, comprising a chamber with an inlet and an outlet and dividers therebetween creating subchambers, each subchamber having a source of ultraviolet light disposed therein, and means for controlling flow including flow through subchambers and means for controlling radiation to the fluid, such as when the subchambers are closed and flow is interrupted, and not when the subchambers are open such as during periods of flow it thereinto or therefrom.
Nebel teaches a method for producing highly purified pyrogen-free water comprising dissolving ozone in water, separating the gas and liquid phases, and exposing the ozone-containing water to ultraviolet radiation to destroy pyrogen in the water.
Bircher et al. teaches a process for treating aqueous waste or groundwater contaminated with nitro-containing organic chemicals to degrade the compound sufficiently to permit disposal of the waste or groundwater.
Johnston teaches a process for removing halogenated organic compounds from contaminated aqueous liquids which comprises contacting the contaminated liquid with a photocatalyst while simultaneously exposing the contaminated liquid to both acoustic energy and light energy to efficiently decompose the halogenated organic compounds.
Mass teaches a reactor for the treatment of a fluid with a substantially uniform dosage of light from a line-type light source, and not a blackbody radiator, in a reactor housing with a central photochemical treatment region.
LaCrosse teaches an ultraviolet-enhanced ozone wastewater treatment system in which ozonated water is mixed within a multi-stage clarifier system with wastewater to be treated and suspended solids are removed. The clarified effluent is filtered and exposed to ultraviolet radiation. Ozone is injected into a contact tower, where reaction takes place, and the UV irradiated, ozonated and clarified liquid is recirculated through an ozone injector and discharged through a mixer plate into a purge chamber, from where a portion is re-diverted to the system and a portion is discharged through a diverter valve through a carbon filter and out the system.
Hinson et al. teaches a two-stage, multiphase apparatus for the purification of water which may contain solid wastes. Gaseous oxidant comprising ozone and oxygen initially removes the solids, and then resaturation with oxidant breaks down and destroys chemical and biological contaminants, prior to UV radiation, degassification and rejection from the system.
Coate et al. teaches a portable system which minimizes the addition of solids to be disposed of through the use of ozone for contaminant reduction to basic elements after the pH value of the waste water to be treated is properly adjusted. Ozone is combined with ultrasound to cause coagulation and precipitation. In another stage, ozone and UV light are used in a reduction process. Ion alignment using a magnetic field and an electrochemical flocculation process to which the waste water is subjected causes further coagulation and precipitation.
Okuda et al. teaches decomposition of an organochlorine solvent contained in water by adding at least one of hydrogen peroxide and ozone to the water and then radiating ultraviolet rays to the water. A catalytic amount of a water-insoluble barium titanate substance is caused to co-exist in the water.
Szabo teaches a UV based water decontamination system with dimmer-control, in which a UV based or dual mode water system operates under household water pressure to provide a batch treatment of contaminated water. Treated water is stored in a pressurized reservoir from which it may be released for use. A pressure drop, or discharge of a sufficient amount of the treated water initiates another treatment cycle. A pressure gauge linked to a UV lamp dimmer detects the pressure drop and causes the UV lamp output to change from a reduced-output, standby mode to an operative mode. lamp output is also linked to filter backwash. The UV light may also be used to produce ozone which is placed in contact with the fluid through a helical tube.